Spring with a mass at an angle, need original length of spring

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Homework Help Overview

The discussion revolves around a physics problem involving a 5 kg mass on a 45-degree incline, connected to a spring with a spring constant of 20 N/m. The objective is to determine the original, unstretched length of the spring when the mass is detached and the spring is at rest.

Discussion Character

  • Exploratory, Assumption checking

Approaches and Questions Raised

  • The original poster attempts to calculate the forces acting on the mass and the spring, using Hooke's law and trigonometric relationships to find the unstretched length of the spring. They express confusion regarding the resulting length calculation, which suggests a negative measurement for the unstretched spring length.
  • Some participants question the accuracy of the problem setup and the values used, including the spring constant.
  • One participant suggests drawing a Free Body Diagram to clarify the forces involved.
  • Another participant indicates that the question may contain errors based on their discussions with others.

Discussion Status

The discussion is ongoing, with participants exploring the problem setup and questioning the assumptions made. There is no explicit consensus on the correctness of the problem, but some productive directions have been provided, such as the suggestion to draw a Free Body Diagram.

Contextual Notes

Participants are considering the implications of the spring constant value and the geometry of the setup, which may affect the calculations. There is uncertainty regarding the accuracy of the problem statement itself.

2Dark4u
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Homework Statement



The Setup is depicted in the Attachment. Essentially there is a 5kg Mass on an incline (45). The incline measures 0.4m from the mass to the corner were it turns 90 degrees and measures 0.3m to were there is a spring (k = 20N/m. This spring attaches to the Mass. This system is in equilibrium with the spring stretched out as it is.

The question is what is the length of the Spring not stretched. As in if the mass was un attached and the spring was at rest?

Homework Equations


Only relevant equation i can think of is F = k(λx) Basic Hookes law

The Attempt at a Solution



So first thing I did
5* 9.8 = 49N

Then 49cos(45) to get Fx of mass = 34.65N this should equal the X component of the force of the spring.

Second the spring should measure 0.5 since it makes a triangle right triangle with 0.4 and 0.3 this also means the angle its at in relation to the x component of force is 36.87

so F of the spring should be Fx = F cos(36.87)

34.65N / cos( 36.87) = 43.31N

then F = k λx and F/k = λx

43.31/20 = 2.16m

Now if the spring stretch measures 0.5m I don't see how λx can equal 2.16m

That would mean that the spring has a negative measurement when unstretched and that doesn't make any sense.

So help me out, were did I go wrong.
 

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2Dark4u said:

Homework Statement



The Setup is depicted in the Attachment. Essentially there is a 5kg Mass on an incline (45). The incline measures 0.4m from the mass to the corner were it turns 90 degrees and measures 0.3m to were there is a spring (k = 20N/m. This spring attaches to the Mass. This system is in equilibrium with the spring stretched out as it is.

The question is what is the length of the Spring not stretched. As in if the mass was un attached and the spring was at rest?

Homework Equations


Only relevant equation i can think of is F = k(λx) Basic Hookes law

The Attempt at a Solution



So first thing I did
5* 9.8 = 49N

Then 49cos(45) to get Fx of mass = 34.65N this should equal the X component of the force of the spring.

Second the spring should measure 0.5 since it makes a triangle right triangle with 0.4 and 0.3 this also means the angle its at in relation to the x component of force is 36.87

so F of the spring should be Fx = F cos(36.87)

34.65N / cos( 36.87) = 43.31N

then F = k λx and F/k = λx

43.31/20 = 2.16m

Now if the spring stretch measures 0.5m I don't see how λx can equal 2.16m

That would mean that the spring has a negative measurement when unstretched and that doesn't make any sense.

So help me out, were did I go wrong.

I wonder if k was supposed to equal 20 kN/m
 
correction ! sorry
 
Draw a Free Body Diagram for the 5 kg block.

attachment.php?attachmentid=45157&d=1331882305.jpg
 
Ive checked with everybody. And so far what people have been able to tell me is that it just looks like the question has to be wrong

I did draw the diagram, its how i saw were all the forces were going. Unless I messed it up somehow.
 
Last edited:

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